Geographic Range

Grand Cayman rock iguanas, Cyclura nubila lewisi, are endemic to the Caribbean island of Grand Cayman. They were formerly widespread in dry and coastal habitats throughout the island, but due to severe habitat loss and predation, they are now found only in the High Rock-Battle Hill area to the east and south of the Queen’s Highway. (Burton, 2004a; "ARKive Images of Life on Earth", 2011)

Habitat

Grand Cayman rock iguanas are ground dwelling and may occupy a number of habitats including forest, grassland, and coastal regions, as well as human-modified habitats. They mainly occur in natural xerophytic shrubland and along the interfaces between farm clearings and canopy dry forest. Farms provide a variety of resources such as vegetation, fallen fruit, and nesting soil. (Burton, 2004a; Burton, 2009; Goodman, 2005)

Grand Cayman rock iguanas spend their nights in retreats such as caves and crevices found within eroded rock, usually heavily eroded limestone. Although iguanas preferentially select natural rock substrate for retreat, they also utilize artificial retreats such as piles of construction material and spaces under buildings. Whereas adults are primarily terrestrial, younger individuals tend to be more arboreal. Occasionally, Grand Cayman ground iguanas may retreat in tree hollows or exposed on tree limbs. (Blair, 1991; Burton, 2009; Goodman, 2007)

Grand Cayman rock iguanas are characterized by even, stiff dorsal spines and a spineless dewlap. Their body is covered in scales, and some enlarged scales are present on the head region. Young iguanas have a gray base color with alternating dark gray and cream chevrons. As they mature, the juvenile pattern fades, and the hatchling base color is replaced by a blue-gray base complexion. Some dark chevrons are retained in adulthood. This blue-gray color is typical of ground iguanas when resting. However, ground iguanas are better known for the stunning shades of turquoise blue they take on during the mating season. For this reason, C. nubila lewisi is also known as the blue iguana. (Burton, 2004b; "ARKive Images of Life on Earth", 2011)

Sexual Dimorphism

male larger

Range mass

>11 (high) kg

lb

Range length

>1.5 (high) mm

in

Development

Grand Cayman rock iguanas lay their eggs in a nest chamber that is dug about a foot below the surface of the soil. While in the nest, eggs take up moisture from the earth. They gradually fill out until they are tight and under slight pressure. On average, Cyclura eggs are among the largest of all lizards. Eggs hatch in 65 to 100 days depending on temperature. The process of hatching may take longer than 12 hours. Hatchlings cut through the leathery egg shell using a microscopic “egg tooth” on the tip of their jaw. (Burton, 2009)

The combined effort of many hatchlings is required to dig out of the nest chambers. Occasionally Ground Cayman rock iguanas do not emerge from the next chamber for as long as two weeks after hatching. Throughout this period, hatchlings survive off of the remaining egg yolk stored inside their abdomen. They can live off of yolk remains for weeks before needing to feed or drink. (Burton, 2009)

Young iguanas are independent after hatching. They tend to be arboreal and spend most of their young life in trees in order to avoid terrestrial predators. (Burton, 2009)

Reproduction

Grand Cayman rock iguanas are solitary except during the mating season. Mating is generally polygamous, but some individuals may also be promiscuous or monogamous. During the breeding season, the home range of a dominant male frequently overlaps that of one or more females. (Blair, 1991; Burton, 2009)

Throughout the breeding season, Grand Cayman rock iguanas take on an intense blue coloration. In the spring, hormones surge and males begin to reassert dominance. Males lose weight during this time, as they devote their energy to breeding and dominating other males. Males expand their territory range, attempting to monopolize as many female territories as possible. Males in overlapping territories challenge each other, and, in most cases, smaller iguanas flee from larger individuals. Physical contact and fighting is rare and is usually restricted to individuals of similiar size. Fights can be vicious and bloody. Toes, tail tips, crest spines, and chunks of skin may be torn off in combat. ("Blue Iguana Recovery Program, Grand Cayman, Cayman Islands, British Indies", 2011)

By March, the abdomen of female Grand Cayman rock iguanas is swollen, as their eggs have formed inside them. They do not become receptive to breeding until late April. Females generally avoid males until they begin to mate in May, retreating into their rock holes whenever males are nearby. Gravid females reduce food intake about 2 weeks before oviposition, because their digestive tract is squeezed by the expanding mass of eggs. They also increase activity levels during this time. (Blair, 1991; Burton, 2009)

Copulation is preceded by a mating ritual. A male bobs its head then circles around behind a female. He grasps the nape of her neck and attempts to restrain her. The male maneuvers his tail under that of the female and positions himself for intromission. Copulation rarely lasts longer than 30 to 90 seconds, and a pair rarely mates more than once or twice per day. Mature pregnant females display a distended abdomen, and the outline of individual eggs may be seen. (Blair, 1991)

The breeding season of Grand Cayman rock iguanas lasts 2 to 3 weeks between late May and mid June. Oviposition occurs approximately 40 days after fertilization, generally during the months of June and July. Females lay 1 to 22 eggs each year. Clutch size varies with age and size of females. Older, larger females are able to produce more eggs. Eggs are then incubated in the nest chamber that is dug about a foot below the surface of the soil. Incubation period ranges from 65 to 90 days. Temperature within the nest remains relatively constant at 30 to 33 degrees Celsius throughout this period. Grand Cayman rock iguanas usually begin breeding around 4 years of age in captivity. In the wild, they reach sexual maturity between 2 and 9 years of age. (Blair, 1991; "Blue Iguana Recovery Program, Grand Cayman, Cayman Islands, British Indies", 2011; Burton, 2004a; Parr, 2010; "ARKive Images of Life on Earth", 2011)

Copulation occurs from late May until mid June. Egg-laying occurs approximately 40 days later in the months of June and July.

Range number of offspring

1 to 22

Average gestation period

40 days

Average time to independence

0 minutes

Range age at sexual or reproductive maturity (female)

2 to 9 years

Range age at sexual or reproductive maturity (male)

2 to 9 years

Female Grand Cayman rock iguanas often travel outside of their normal range to locate suitable nesting areas. Nest burrows are dug in sand or soil exposed to the sun. Several days before laying their eggs, females begin to dig in preparation for building their nests. It may take an entire afternoon to excavate a complete nest burrow. Female ground iguanas remain in nest burrows overnight to lay their eggs. While most emerge the following morning, some females remain underground for up to 2 days while laying their eggs. A female iguana fills the nest burrow with sand until a large mound is formed over the nesting site. She then scatters leaves over the area until the nest is completely disguised. When the nest is secure, she allows herself to feed again but remains close to the next. Females guard their next site for several weeks to prevent other iguanas from using the area for nesting and to protect from predators. Hatchlings are vulnerable to native snakes, such as Alsophis cantherigeruscaymanus, and suffer an extremely high mortality rate.

Lifespan/Longevity

It is believed that Grand Cayman rock iguanas are among the longest lived species of lizard. In the wild, they are thought to reach ages of at least 25 to 40 years. However, rock iguanas can grow much older when kept in captivity. The longest living member of this species was a captive iguana known as “Godzilla” who survived to an estimated 69 years. It is doubtful, however, that wild iguanas can survive to this age, because Godzilla required extraordinary maintenance in the years before his death. (Adams, 2004; Blair, 1991)

Range lifespanStatus: captivity

69 (high) years

Typical lifespanStatus: wild

25 to 40 years

Behavior

Grand Cayman rock iguanas spend the majority of the daytime basking in the sun. They are mainly inactive with low to moderate alertness between morning emergence and evening retreat. During activity, iguanas primarily forage, travel, and inspect substrates, including retreats and feces. Iguanas are active for longer periods of time during the summer. Because they are ectothermic, the greater amount of sunlight and higher temperatures during the summer allows iguanas to maintain optimal body temperatures for a longer period each day. ("Blue Iguana Recovery Program, Grand Cayman, Cayman Islands, British Indies", 2011; Goodman, 2007)

Home Range

Grand Cayman rock iguanas are solitary and primarily occupy regions of forest rock and forest soil. Iguanas may become aggressive at a very early age. Female iguanas establish and maintain a small, stable home range during the course of their lives. Females stay close to their retreats and occupy a small territory of about 0.6 acres. Their home range includes places to bask and feed and an area of soil deep enough to nest in. They defend their territory from other iguanas. Iguanas use head bobbing gestures to warn intruding iguanas and may even attack the intruder. In contrast with female iguanas, male ground iguanas occupy much larger territories, about 1.4 acres, and they tend to occupy larger territories as they grow. Males often have several sleeping holes scattered around their territories. ("Blue Iguana Recovery Program, Grand Cayman, Cayman Islands, British Indies", 2011; Burton, 2004b; Burton, 2006; Goodman, 2005)

Food Habits

Grand Cayman rock iguanas are primarily herbivorous, consuming mostly plant matter from at least 45 plant species in 24 different families. Leaves and stems are consumed most frequently, while fruits, nuts, and flowers are consumed in smaller quantities. Carnivory makes up a small percentage of the diet. This includes predation of invertebrates such as insects, slugs, and moth larvae. Grand Cayman rock iguanas have also been observed ingesting small rocks, soil, feces, bits of shedding, and fungi. (Burton, 2009; Goodman, 2007; Parr, 2010; "ARKive Images of Life on Earth", 2011)

Predation

Young Grand Cayman rock iguanas are heavily preyed upon by a variety invasive species, including feral cats, mongooses, dogs, rats, and pigs. Predation by feral exotics is regarded as one of the major threats to the species and is greatly responsible for the critical population decline. Rats can cause severe injury to hatchlings and may cause mortality. The primary native predator of hatchlings is Alsophis cantherigerus. Adult Grand Cayman rock iguanas have no natural predators, but they are threatened by roaming dogs. Adults are also trapped and killed by humans. Ground iguanas may use head bobbing to scare away predators. (Alberts, 2007; Burton, 2004a; Burton, 2009; "ARKive Images of Life on Earth", 2011)

Economic Importance for Humans: Negative

Conservation Status

Cyclura nubila lewisi is one of the fastest disappearing and most critically endangered species on Earth. The decline of Grand Cayman rock iguanas likely began in pre-Colombian times when they were hunted for food by native Indians of the Arawak and Lucayan tribes. More severe decline began with European settlement of the Cayman Islands. As the human population increased, extensive habitat was cleared for agriculture as well as residential and commercial developments. Today, habitat loss is the main factor threatening extinction of Grand Cayman rock iguanas. Construction of vehicular roads resulted in further habitat destruction and has brought fast-moving traffic into remnant habitats. This occasionally results in vehicular deaths. (Blair, 1991; Burton, 2004a; "ARKive Images of Life on Earth", 2011)

Another major threat associated with European settlement was the introduction of invasive species to the island, such as cattle, goats, pigs, rats, cats and dogs. Grand Cayman rock iguanas face predation by or competition with these introduced animals. Less frequently, iguanas may be illegally trapped or shot at by farmers who perceive iguanas as a threat to their crops. (Blair, 1991; Burton, 2004a; Burton, 2009; "ARKive Images of Life on Earth", 2011)

Grand Cayman rock iguanas are fully protected under local legislation and are considered critically endangered by the IUCN. It is illegal to kill, capture, or hold members of this species in captivity. Furthermore, international trade of this species is prohibited, as it is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES). (Burton, 2004a; "ARKive Images of Life on Earth", 2011)

Contributors

Laura Malmut (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, Gail McCormick (editor), Animal Diversity Web Staff.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

diurnal

active during the day, 2. lasting for one day.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

island endemic

animals that live only on an island or set of islands.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

Blair, D. 1991. "West Indian Iguanas of the Genus Cyclura: Their Current Status in the Wild, Conservation Priorities and Efforts to Breed Them in Captivity"
(On-line pdf).
Accessed
March 06, 2011
at http://www.vipersgarden.at/PDF/DB_Cyclura.pdf.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.